1. Field of the Invention
The present invention relates to recording and reproduction of a video signal, and in particular, it relates to a VCR of helical scan type.
2. Description of the Related Art
Among apparatus for recording and reproducing video data, the main stream has been the so-called helical scan VCR, in which recording is made by scanning a magnetic head mounted on a rotary drum diagonally with respect to a tape.
Video signals are transmitted in a signal format having a constant periodicity. Therefore, apparatus for recording and reproducing them is equipped with a mechanical recording system that synchronizes with the video signals. To be concrete, 30 frames of images are transmitted each second in the NTSC method, and a VCR that records them rotates a rotary drum 30 times a second, so as to record the image of one frame at every rotation. Or, the VCR is adapted for the segment recording method, in which each frame is recorded by dividing it with a rotational speed of an integral multiple (150 revolutions for instance). The former is a recording method used mainly for analog VCR""s, and the latter is a recording method mainly used for digital-video VCR""s.
With regard to a recording tape pattern, the recording is made in such a track pitch that reduces amount of tape usage taking into consideration a mechanical accuracy, an error due to deformation of a tape, and so on.
It is generally taken as a guide that a width of recording tracks is twice the width of a minimum track, from which recorded signals can be reproduced, in order to realize compatibility of reproduction.
Described hereinafter, as an example, is a conventional VCR for broadcasting use abiding by the D-7 format of the SMPTE (i.e. Society of Motion Picture and Television Engineers) standard, with a tape of 6.35 mm width.
The conventional VCR for broadcasting use forwards a tape of 6.35 mm width at a speed of 33.8 mm/sec. It performs the so-called one-channel recording with a pair of heads mounted on a rotary drum of 21.7 mm in diameter, which rotates at 9,000 rpm (revolutions per minute). It records one frame of NTSC video data by dividing it into ten tracks (i.e. segment recording).
A track pitch for each of the tracks is 18 xcexcm. This is a so-called guard-bandless recording method in the azimuth recording, and a width of the tracks is same as the track pitch.
Information to be recorded are video data compressed into approximately 25 Mbps and audio data of approx. 1.5 Mbps. A total recording rate is 41.85 Mbps after an ECC (error correction code), a SYNC (synchronous) data, an ID data, and the like are added to the video data and the audio data.
Although the track width virtually needed for recording and reproduction is approx. 9 xcexcm in this instance, the track pitch is normally set for 18 xcexcm, in consideration of reproduction compatibility, envelope variation, output reduction and dispersion of performance due to an environmental change, and editing of images. As a result, it is possible to reproduce the tracks of 9 xcexcm width in the worst case even if interchanged reproduction and interchanged editing are made with a different VCR.
There are also occasions that HD signals of higher image quality than the NTSC signals are recorded using a basic mechanism of the conventional VCR for broadcasting use. In such cases, the HD signals of one frame is compressed into 100 Mbps, and recorded in four recording tracks (four-channel recording) at every half turn of the rotary drum comprising two combinations of four recording heads. Tape speed is 135.2 mm/sec.
In this instance, one frame of the compressed video data is recorded by dividing it into 40 tracks. A track pitch for each of the tracks is 18 xcexcm. Compatibility of reproduction with other apparatus can be ensured under all circumstances when recording is made with the track pitch of 18 xcexcm.
Although the apparatus can be adapted for the higher image quality by employing the recording head for four channels (xe2x80x9cchxe2x80x9d), a recording time decreases to one-fourth, as it uses quadruple the tape needed for the 1-ch recording. In other words, a cost of the tape goes up.
It is therefore desired that use of tape be reduced by narrowing the track pitch (narrowed track), so as to realize a long-hour recording, and reduction of the tape cost.
However, there occurs a slim-out of the tracks and incomplete erasing, when a cut editing and a link editing are made on the tape with a VCR adapted for the narrowed track (a track pitch of 9 xcexcm, for instance) in the conventional format. Consequently, a problem results in that the VCR is unable to reproduce the tracks around the edited spot. There is also a probability of erasing a track preceeding the editing IN spot, or failing to erase a track being edited right after the IN spot, when, for instance, a cut editing is being made.
The present invention was derived in consideration of the foregoing problem.
A magnetic recording and reproducing apparatus of the present invention is a helical scan type magnetic recording and reproducing apparatus for recording data of vide signal on a sync-block by sync-block basis in an N number (Nxe2x89xa73, and N represents a natural number) of tracks in one frame period on a magnetic tape with a rotary magnetic head, and the apparatus comprises:
a rotary drum unit for driving the rotary magnetic head;
a tape driving unit for driving the magnetic tape;
an encoding section for executing a data compression process on video data on per-frame basis, and outputting a plurality of the compressed video data;
an ECC adding section for adding an error correction code to each of the plurality of compressed video data;
a sync block generating section for producing a plurality of first sync block data in which a synchronizing code and an identification code are added to each of the plurality of compressed video data;
an auxiliary data generating section for producing an auxiliary data;
a recording processor for executing a process of digital recording the plurality of first sync block data and the auxiliary data on the magnetic tape; and
a controller for controlling an input of the plurality of first sync block data and the auxiliary data into the recording processor.
The tape driving unit drives the magnetic tape at a first speed. The controller controls in such a manner that the auxiliary data is recorded in two tracks at both ends of the N number of tracks, and the plurality of first sync block data are recorded in the tracks other than the two tracks at both ends of the N number of tracks. Accordingly, the apparatus records the video signal on the magnetic tape in a track pitch that is narrower than the standard track pitch.
Further, the magnetic recording and reproducing apparatus of the present invention is adapted to use a correction code of larger length when recording in the narrow track pitch than that of the standard track pitch.